In ion implantation of semiconductor wafers and other processes in which a beam of particles or radiation is directed at a workpiece through a vacuum, it is necessary to support the workpieces in an array on a support element (e.g., a spinning disk), and the support element is moved with respect to the beam, usually in two directions.
The vacuum chamber must either house the drive equipment or the drive equipment must be introduced from the outside. Housing the drive equipment in the vacuum chamber presents problems of contamination of the vacuum environment with grease, etc., and makes the chamber large and costly to pump down after opening. Driving the equipment from outside has caused mechanical complexity and expense and has made it difficult to introduce cooling water and the like to the wafer support members.
Some conventional beam-treatment devices employ planar vacuum seals consisting of two very smooth (optically flat) planar surfaces that move relative to one another without making contact. The smooth plates required are extremely expensive, particularly when large enough to accomodate several inches of relative movement. This cost makes them unattractive for many applications. To maintain a vacuum with such devices, the gap between the two smooth surfaces is pumped from a plurality of positions.
In other evacuated beam devices, such as electron microscope sample stages, sample position is adjusted a small distance (e.g., one inch) by sliding a single annular seal against a planar surface. To maintain a vacuum, the seal is very tightly compressed against the surface. The seal compression force results in very large frictional resistance to movement, but because beam position adjustments are made slowly and infrequently the friction is of little consequence.